The casting of certain ingots of, for example, titanium alloys and certain other high performance alloys, may be both expensive and procedurally difficult given the extreme conditions present during production and the nature of the materials included in the alloys. For example, in many currently available cold hearth casting systems, such as plasma arc melting in an inert atmosphere or electron beam melting within a vacuum melt chamber, the casting system can be used to melt and mix various recycled scrap, master alloys, and various other starting materials to produce the desired alloy. The casting systems utilize starting materials that can contain high density and/or low density inclusions, which in turn can lead to a lower quality and potentially unusable heat or ingot. Cast material considered unusable oftentimes can be melted down and reused, but such material typically would be considered of lesser quality and command a lower price in the marketplace. During casting operations, producers generally desire to remove inclusions from the molten material prior to directing the molten material into the casting mold.
To vaporize, dissolve, or melt inclusions in molten material, an energy source in the casting system, such as an electron beam gun or plasma torch, for example, can apply energy to the surface of molten material in a hearth of the casting system. The energy produced by the energy source can be sufficient to vaporize or melt the inclusions. However, during casting operations, a dynamic flow path can develop in the hearth of the casting system, and less dynamic regions, i.e., stagnant zones or pools, can form adjacent to, around, and/or near the dynamic flow path. Without adequate mixing, molten material can rest in a stagnant zone, and thus remain in the hearth, for a longer period of time than the molten material flowing along the dynamic flow path. In other words, the residence time of molten material in the hearth can depend on whether the molten material flows along the dynamic flow path or rests in a stagnant zone, and thus, the residence time of molten material in the hearth can be inconsistent. Furthermore, the molten material in stagnant zones can be subjected to the energy produced by the energy source for a longer period of time than the molten material in the dynamic flow path. As a result, the elemental depletion of molten material having a longer residency time in the hearth, i.e., molten material that rests in a stagnant zone, can be greater than the elemental depletion of molten material having a shorter residency time in the hearth, i.e., molten material that flows along the dynamic flow path. When the molten material in the hearth has different chemical compositions throughout, the resulting cast alloy can have compositional variances.
Furthermore, in casting systems that utilize multiple casting molds extending from a single hearth, the formation of stagnant zones can divert and/or alter the desired flow of molten material into the casting molds. In other words, the casting rates can vary between the casting molds of the casting system.
Accordingly, it would be advantageous to provide a casting system that is less susceptible to the formation of stagnant zones in the hearth thereof. Further, it would be advantageous to provide a casting system that produces a more compositionally uniform cast alloy. Additionally, it would be advantageous to provide a casting system that promotes identical or similar casting rates across multiple casting molds. More generally, it would be advantageous to provide an improved casting system that is useful for titanium, other high performance alloys, and metals and metal alloys generally.